The invention relates to a method for generating and applying/conducting at least one voltage pulse, which provides a cleaning effect for a stop switch, to a stop connection assigned to said stop switch, which stop connection is provided on a digitally controlled magnetic ignition circuit of an electrical device, wherein the magnetic ignition circuit generates a voltage wave series from half waves, the amplitude of which decreases over time, and/or generates at least one voltage pulse in a medium voltage range. The invention further relates to a digitally actuated/controlled or actuable magnetic ignition circuit of an electrical device, said circuit comprising a stop connection assigned to a stop switch, wherein the magnetic ignition circuit is embodied for generating and applying/conducting at least one voltage pulse, which provides a cleaning effect for the stop switch, to the stop connection, and wherein the magnetic ignition circuit is embodied for generating a voltage wave series from half waves, the amplitude of which decreases over time, and/or for generating at least one voltage pulse in a medium voltage range.
Many electrical devices or machines contain stop switches that are provided with contacts or contact surfaces; one problem with such contacts or contact surfaces is that they can become contaminated, for example, oxide layers can form on the switch contacts. It therefore makes sense for the switch contacts or switch contact surfaces to be cleaned regularly or occasionally, by at least removing the thin oxide layers, so as to ensure the proper functioning of the stop switch. With many other contaminants, cleaning by deposit burning off, for example, is unfortunately not yet an option.
The prior art contains various approaches for cleaning such switches. For example, it is known to clean switches using sliding contacts. In such processes, sliding switches are used for self-cleaning the contact surfaces. When the switch is activated, one contact slides over the other, with this sliding movement removing contaminants of all types from the contact surfaces. This is intended to ensure a reliable contacting of the contact surfaces. The contact surfaces are scrubbed clean each time the switch is activated.
Another concept involves switch cleaning using high-voltage pulses. In this case, the contact surfaces on the two switch surfaces are cleaned using high-voltage pulses. The high-voltage pulses are a byproduct of a high-voltage stop. With this type of stop, the charging coil of an ignition circuit in the electrical device is short-circuited. This prevents an ignition capacitor, which is also provided in the ignition circuit, from charging. It is therefore impossible to generate an ignition spark. With the method of the high-voltage stop, a very high pulsed voltage is applied to the stop connection. If the stop contact is touched, an electric shock can occur. As a result, the stop circuit must be insulated through costly methods and means. Nevertheless, because of the high voltage, the switch contacts are self-cleaned whenever the stop switch is pressed. A device of this type is known, for example, from DE 10 2004 059 070 A1. The peak voltages generated in this case lie at around 250 V.
Older analog ignition circuits frequently have a separate coil for stopping. In such cases, when the stop switch is pressed voltage no longer builds up at an ignition capacitor of the analog circuit, and the igniter will no longer spark. This is achieved by positioning the charging coil and the breaker coil in the same alignment on a metal core. As a result, the voltage is cophasal, and whenever the charging coil is to be charged, said voltage passes through a thyristor, correspondingly provided in the circuit. The voltage occurring at the shut-off coil results in a medium voltage at the stop connection.
One problem with this method, however, is that the last spark is generated at an uncontrollable time, and therefore the probability of a misfire is very high.
With digital ignition circuits, rather than an analog igniter, an igniter controlled by a microcontroller is used. For this purpose, in addition to the above-described high-voltage stop, the concept of the low-voltage stop is available, however, the low-voltage stop, in which voltage pulses in the voltage supply range of digital control or below are used, exerts no cleaning effect on the switching contacts of the stop switch. This method does not involve any self-cleaning of the contacts.
U.S. Pat. No. 4,976,234 A, U.S. Pat. No. 4,697,570 A, US 2008/252219 A1, U.S. Pat. No. 4,610,237 A and DE 200 14 502 U1 disclose stop switches for internal combustion engines and/or ignition systems. Devices for switch cleaning are not described.
Therefore, the problem addressed by the invention is that of specifying a method that is improved in this respect or a digitally controlled or controllable magnetic ignition circuit that is improved in this respect.